What is the cleanest way to increment an Integer in an ArrayList?
ArrayList<Integer> ints = new ArrayList<>();
ints.add(5);
ints.add(9);
What is the cleanest way to increment the last element?
ints.set(ints.size() - 1, ints.get(ints.size() - 1) + 1); seems pretty ugly to me.
You can't increment the value in place since Integer objects are immutable. You'll have to get the previous value at a specific position in the ArrayList, increment the value, and use it to replace the old value in that same position.
int index = 42; // whatever index
Integer value = ints.get(index); // get value
value = value + 1; // increment value
ints.set(index, value); // replace value
Alternatively, use a mutable integer type, like AtomicInteger (or write your own).
Maybe you need to use another structure of data?
LinkedList<AtomicInteger> ints = new LinkedList<AtomicInteger>();
ints.add(new AtomicInteger(5));
ints.add(new AtomicInteger(9));
ints.getLast().incrementAndGet();
I have done something like this:
arraylistofint.set(index, arraylistofint.get(index) + 1);
here is an example from my code (modified names):
ArrayList<Integer> numBsPerA = new ArrayList<> ();
...
int cntAs = 0;
int cntBs = 0;
for ( TypeA a : AnArrayListOfAs )
{
numBsPerA.add(0);
for ( TypeB b : a.getAnArrayListOfBs() )
{
numBsPerA.set(cntAs, numBsPerA.get(cntAs) + 1);
cntBs++;
}
System.out.println(a.toString()+ " has "
+numBsPerA.get(cntAs)+" TypeBs");
cntAs++;
}
System.out.println("Total number of As: "+cntAs);
System.out.println("Total number of Bs: "+cntBs);
// can now loop over numBsPerA to check how many Bs per A or whatever.
I can done by the code using java ...In that we can Increment each element of the list
List<Integer> list= new ArrayList<Integer>();
//int[] primitive = List1.toArray(list1);
int count=0;
int count1=0;
int k=0;
list.add(3);list.add(2);list.add(3);list.add(5);
System.out.println("The given input is");
for(int i:list){
System.out.println(i);
}
Integer[] a = list.toArray(new Integer[list.size()]);
for(int i = 0; i <a.length; i++)
{
if(i==a.length-1){
a[i]++;
count++;
}else if(i==a.length-2){
a[i]++;
count++;
}else if(i==a.length-3){
a[i]++;
count++;
}else if(i==a.length-4){
a[i]++;
count++;
}
}
System.out.println("After first operation");
for(int i:a){
System.out.println(i);
}
System.out.println("the first count is"+count);
for(int i = 0; i <a.length; i++)
{
if(i==a.length-1){
a[i]--;
count1++;
}else if(i==a.length-2){
a[i]--;
count1++;
}else if(i==a.length-3){
a[i]--;
count1++;
}else if(i==a.length-4){
a[i]--;
count1++;
}
}
for(int i:a){
System.out.println(i);
}
System.out.println("the second count is"+count1);
//int Count2=count+count1;
System.out.println("After second operation");
System.out.println("--------------------------------------------");
for(int j:a){
System.out.println(j);
}
List<Integer> list1=Arrays.asList(a);
System.out.println("After conversion of list");
for(int i:list1){
System.out.println(i);
}
i made the count also...
This question asked in one of the interview also..
int[] ints = new int[10];
++ints[9];
// or
++ints[ints.length - 1];
Note: however, usually, it is safer to stick to the List.
private static void increment(List<Integer> list, int ind) {
list.set(ind, list.get(ind) + 1);
}
List<Integer> list = new ArrayList<>();
list.add(5);
list.add(15);
increment(list, list.size() - 1);
Note: even if you need to increment only one time in one function, it may be worth it to have such a snippet for readability.
